Method and apparatus for variable density inking

Abstract

The present invention is directed to a variable density inking apparatus for use in a lithographic press, letter press, flexographic system or the like. The apparatus includes an anilox roll, means for feeding metered quantities of ink to the anilox roll surface, and a printing roll. A form roll is in peripheral engagement with the anilox roll and in ink delivering relation to the printing roll or to a further form roll. A characterizing feature of the invention lies in the provision of means for driving the form roll and anilox roll in the same direction while permitting relative speed variations in peripheral speed between the noted rolls in a ratio of from 1:1 to about 3:1 in either sense, thereby to enable an infinite variation in printing density.

Having thus described the invention and illustrated its use, what is claimed as new and is desired to be secured by Letters Patent is: 
     
       1. A variable density inking apparatus for a printing apparatus employing a celled ink metering roll such as a letter press or lithographic press comprising ink fountain means, an anilox roll mounted in ink receiving position relative to said fountain means, said anilox roll including a multiplicity of outwardly open cells on the periphery thereof, metering means wipingly engaging the surface of said anilox roll for removing therefrom ink film externally of said cells, a printing roll rotatable relative to said anilox roll, at least one resilient form roll interposed between said printing roll and said anilox roll, said form roll being in peripheral contact with said printing roll and being pressed against said anilox roll to indent into said cells of said anilox roll, said anilox, form, and printing rolls being rotatable about parallel axes, the contacting portions of said rolls rotating in the same direction, the combination including means for varying the relative peripheral speed of said form and anilox rolls in the range of from about 1:3 to 3:1. 
     
     
       2. Apparatus in accordance with claim 1 wherein said ink metering means comprises a doctor blade engaging the surface of said anilox roll at a negative rake angle. 
     
     
       3. Apparatus in accordance with claim 1 and including a second forming roll engaging said anilox roll at a position spaced from the position of engagement between said anilox roll and said at least one form roll, the contacting portions of said second form roll and anilox roll moving in the same direction, the relative peripheral speeds of said second roll and anilox roll being the same as the relative speeds of said anilox and at least one roll. 
     
     
       4. Apparatus in accordance with claim 3 and including an ink transfer roll interposed in ink transferring relation between said printing roll and said at least one form roll. 
     
     
       5. Apparatus in accordance with claim 3 wherein the diameters of said at least one and said second form rolls are different. 
     
     
       6. Apparatus in accordance with claim 1 wherein said means for varying the relative peripheral speed results in said form roll moving at a lower peripheral speed than said anilox roll. 
     
     
       7. The method of varying the ink deposit density of a printing apparatus of the type which includes an ink fountain, an anilox roll having outwardly open cells in the periphery thereof, said anilox roll being disposed in ink receiving relation to said fountain, a doctor blade in wiping engagement to the surface of said anilox roll, thereby to remove ink from said anilox roll in areas external of said cells, at least one resilient form roll coaxially aligned with said anilox roll and in engagement therewith, and a printing roll in ink receiving relation to said form roll, comprising the steps of urging said form roll against said anilox roll, thus to indent the resilient material of said form roll into said cells while simultaneously causing the peripheral portions of said form and anilox rolls to move in the same direction and including a variation in peripheral speeds of said form and anilox rolls from a 1:1 ratio corresponding to a maximum printing density to a ratio of from about 1:3 to 3:1, thereby to reduce the printing density from said maximum. 
     
     
       8. The method in accordance with the claim 7 and including the step of causing the surface of said anilox roll emerging from said fountain to be engaged by a doctor blade inclined at a negative angle relative to said anilox roll, thereby to strip from the surface of said anilox roll ink externally of said cells.